Embodiments disclosed in the present invention relate generally to electrical technology, and more specifically to semiconductors, structures thereof, and methods of forming semiconductor devices.
Semiconductor dies are conventionally enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the semiconductor die and a next level of assembly such as a printed circuit board (PCB) or motherboard. The plastic packages are configured to provide protection of semiconductor die, permit removal of heat generated by the semiconductor die, and permit transmission of electrical signals to and from the semiconductor die.
Ball-grid array (BGA) semiconductor packages are a type of package that uses a laminate substrate, such as a printed circuit board. Depending on the application, the laminate substrate can includes multiple layers of conductive material separated by dielectric layers. The layers of conductive material are patterned to form conductive traces, conductive plane structures (e.g., ground planes and/or power planes), and input/output (I/O) pads, which typically are interconnected with conductive vias. A semiconductor die, such as an integrated circuit, is attached to the laminate substrate with a bonding material and bond wires typically are used to electrically connect pads on the semiconductor die to the conductive traces. Alternatively, the semiconductor die can be attached to the conductive traces or pads on the laminate substrate in a flip-chip configuration. A hard plastic encapsulant material is used to cover the various components and forms the exterior of the semiconductor package, commonly referred to as the package body.
Differential signaling is one known technique for high speed transmission of electrical signals between a packaged semiconductor device and a higher level system. Differential signaling uses two complementary signals sent on two paired wires, called a differential pair. The differential pair technique can be used for both analog signal processing, as in balanced audio as well as digital signal processing, as in RS-422, RS-485, Ethernet over twisted pair, PCI Express, DisplayPort, HDMI, and USB as well as others. In BGA packages, the differential pairs have been implemented with pairs of conductive traces formed on the laminate substrates, and have been implemented using a microstrip or stripline configuration with a dielectric layer separating the differential pairs from one or more conductive plane layers. Certain challenges have existed in achieving good quality high speed signal transfer in semiconductor packages including those that use differential pair configurations. Such challenges have included improving impedance matching, reducing signal reflection and return losses, and maximizing power transfer.
Accordingly, it would be desirable to have a semiconductor package that has improved impedance matching, that reduces signal reflection and return losses, and that maximizes power transfer. It would also be desirable for the semiconductor package to be compatible with existing assembly processes and techniques.
For simplicity and clarity of illustration, elements in the figures are not necessarily drawn to scale, and the same reference numbers in different figures denote generally the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. It will be appreciated by those skilled in the art that words, during, while, and when as used herein related to circuit operation are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as propagation delay, between the reaction that is initiated by the initial action. Additionally, the term while means a certain action occurs at least within some portion of a duration of the initiating action. The use of word approximately or substantially means a value of an element is expected to be close to a state value or position. However, as is well known in the art there are always minor variances preventing values or positions from being exactly stated.